When Sir Harcourt Courtly, the corpulent 57-year-old ‘weather-vane of the beau monde’, decides to take a wife, no one is more certain than he of his base and mercantile intentions. A visit to Oak Hall in Gloucestershire, country seat of the Harkaways, soon changes all of this, however, when the unfashionable matter of love insinuates itself into Sir Harcourt’s brocade-clad bosom; a chase ensues that has very little to do with either foxes or hounds.

Nineteenth-century Irish playwright Dion Boucicault may have slipped from collective memory, but his celebrated London Assurance has retained a well-deserved foothold. It’s a rollicking comedy of manners whose parentage is clearly the Restoration comedies of Congreve and Etherege, yet whose gently good-natured temperament anticipates the developments of Wilde and Shaw. The classic conceit that sees the worlds of country and city collide is played out here with a broad-faced grin, and a requisite cast of fops and feckless heirs apparent prance and preen their way over the stiles and ditches of an unashamedly rustic plot.

Not since Zoe Wannamaker and Simon Russell Beale’s Much Ado About Nothing has the National Theatre seen such a dynamic – and unexpected – love pairing. Taking the roles of Sir Harcourt and his elusive fox-hunting, cigar-smoking innamorata Lady Gay Spanker, Fiona Shaw and Beale are clearly having an absolute blast, and it is to Nicholas Hytner’s credit that his direction gives their anything-you-can-do partnership its head without ever allowing it to run out of control.

Beale’s ageing fop is a bulging-eyed kiss-curled vision of self-satisfaction, with just a hint of vulnerability – repugnant but somehow strangely endearing. Lady Gay is a part that might have been written for Shaw’s wiry physique and throaty chuckle, and I doubt there was a single member of the audience not a little in love with her by the end.

Rounding out an ensemble cast that lacked a single dud are NT regular Michelle Terry as Grace, Sir Harcourt’s intended bride, and Paul Ready as his deliciously limp son Charles. Richard Briers (whose first entrance provoked a spontaneous round of applause) is perfection as Lady Gay’s long-suffering husband Dolly, and Nick Sampson’s Cool – a 19th-century Jeeves with ‘manners above his station’ – also deserves mention.

Mark Thompson’s set-design is a gloriously maximalist affair, complete with crenellations, diamond panes and a remote-controlled rat, who stole the show on two separate occasions. There is nothing half-hearted about this production or this play; the combination of tongue-in-cheek levity and deeply serious talent is intoxicating. Don your britches, grab your whip and join the chase. Tally-ho!

National Theatre, until June 29. Tel: 020 7452 3000 (www.nationaltheatre.org.uk).